1. Field of the Invention
The present invention relates to the technical field of power supply devices, and more particularly to an electromagnetic coupling multi-output control circuit using a coupling coil to increase output voltage, and stabilizing voltage by a control of non-inductive duty cycles to maintain a constant output voltage value, so as to improve energy conversion efficiency.
2. Description of the Related Art
Switching power supply (SPS) generally comes with a fly-back, forward, full bridge, half bridge or push-pull circuit architecture and features the advantages of high efficiency, small volume, light weight, easy installation and large output voltage range, so that the switching power supply can be used extensively in various electronic devices to improve the quality of operations. With reference to FIG. 1 for a power driving device 1 of a display device, a primary side control fly-back conversion circuit architecture is adopted, and the power driving device 1 uses a primary side coil (N1) of a coupling transformer 10 to sense a filtered and rectified input voltage (Vin) to form a primary side current, so that a coil (N2) of the secondary side is affected by the change of the primary side current to sense a first driving voltage (VD1) with an output voltage of 5V, while another coil (N3) of the secondary side is also affected by the change of the primary side current to sense a second driving voltage (VD2) with an output voltage of 28V for driving a plurality of light emitting diodes (LED) of a backlight source.
Due to the instable second driving voltage caused by manufacturing errors of the LED and a change of the input voltage source, the power driving device 1 comes with a stabilizing control circuit 11 connected to the coil (N3), so that a boost control chip 110 can be used to modulate the frequency required for the resonance of an inductor 111 and a capacitor 112 to output a rated voltage. The power driving device 1 requires a set of the stabilizing control circuit 11 for every additional outputting voltage, thus resulting in a more complicated structure and incurring a higher cost.
In view of the aforementioned problems, it is a main subject for the invention to simplify the circuit architecture of the stabilizing control circuit 11 to achieve the function of supplying a plurality of stable output voltages while reducing the cost.